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A recent study published in the Journal of Affective Disorders suggests that greater muscle strength, particularly in women, might play a direct role in reducing the risk of depression and its specific symptoms. Scientists at University College London found no evidence that aerobic fitness influences depression, but their findings indicate that building muscle strength could help prevent and treat the condition. This provides evidence that strength training could be an effective, targeted strategy for improving mental health.
Physical activity is known to help protect against depression, but the exact biological reasons for this connection remain unclear. Scientists wanted to understand the specific ways exercise influences mental health so they can develop better treatment plans.
Two possible ways exercise might improve mood are through better cardiorespiratory fitness and increased muscle strength. Cardiorespiratory fitness refers to the ability of the heart and lungs to supply oxygen to the body during sustained physical activity. Previous studies have linked both of these fitness types to lower rates of depression.
Traditional observational studies, which simply watch people’s habits over time, struggle to prove cause and effect because other lifestyle choices might influence the results. It is also possible that being depressed causes people to exercise less, rather than a lack of fitness causing the depression.
“Although physical activity is known to help prevent and treat depression, the underlying mechanisms through which this occurs remain poorly understood. In this study, we examined the effects of two specific physiological aspects of physical activity (cardiorespiratory fitness and muscle strength) on depression,” said study authors Snehal M. Pinto Pereira, John Vincent, and Amy E. Taylor — a professor, research fellow, and senior research fellow, respectively — in a joint statement to PsyPost.
“Depression is well documented as being a highly heterogeneous disorder, with symptoms varying widely across individuals. Therefore, we examined whether cardiorespiratory fitness and muscle strength might be causally linked to individual symptoms of depression as well as depression as a single disorder.”
The researchers examined data from up to 341,326 adults between the ages of 37 and 73. All participants were of European descent and were part of the UK Biobank, a large database of genetic and health information.
To determine cause and effect, the scientists used a technique called Mendelian randomization. This method looks at tiny genetic variations that people are born with, which are known to be linked to specific physical traits. Because these genetic markers are assigned randomly at conception, they act like a natural experiment.
The scientists looked at genetic variants associated with cardiorespiratory fitness and genetic variants associated with grip strength. Grip strength was adjusted for body weight and used as a practical substitute for overall muscle strength.
For the mental health outcomes, the researchers looked at general depression based on self-reported history and hospital records. They also evaluated nine specific symptoms of depression to get a more detailed picture of a person’s mental state.
These symptoms included depressed mood, appetite changes, concentration problems, and anhedonia, which is a core symptom of depression defined as the loss of pleasure or interest in previously enjoyable activities. They also looked at psychomotor changes, which involve either a noticeable slowing down of physical movements or extreme restlessness and fidgeting.
The individual symptoms were measured using a standard questionnaire given to a subset of 108,622 participants. People who reported experiencing a symptom for several days or more over the past two weeks were considered to have that symptom.
The researchers found no evidence that genetic markers for cardiorespiratory fitness were linked to overall depression or any of its individual symptoms. This was an unexpected outcome for the scientists, as aerobic exercise is often recommended to improve mental health.
On the other hand, the data showed a clear link between greater grip strength and lower rates of depression. A 0.1 kilogram increase in grip strength per kilogram of body weight was associated with a 14 percent lower likelihood of experiencing general depression.
Higher grip strength was also linked to a lower likelihood of several specific symptoms. For example, it was associated with a 21 percent reduction in the likelihood of experiencing anhedonia. Stronger grip strength was also tied to a 44 percent lower chance of experiencing appetite changes. The scientists also found evidence that greater strength is associated with depressed mood, physical slowness, extreme fatigue, and concentration problems.
“Whilst muscle strength is clearly only one of many factors that influence depression, these findings suggest that improving muscle strength could make meaningful contribution to reducing depression as well as several of its symptoms,” the researchers said. “Importantly, the results were consistent across several analyses, which increases confidence in the robustness of the findings.”
When the scientists analyzed the data by sex, they found that these effects were generally stronger in women than in men. The protective effects against loss of pleasure, depressed mood, and concentration problems were observed in females but not in males.
The link between grip strength and appetite changes was present in both men and women. There was no clear evidence that grip strength affected sleep problems or suicidal thoughts in either sex.
“The key takeaway from our findings is that muscle strength (particularly in females) likely plays a causal role in depression and several of its symptoms in middle to older aged adults,” the researchers explained. “Our findings suggest that increasing muscle strength could help reduce depressed mood and the loss of pleasure or interest in previously pleasurable activities (anhedonia), which represent the core symptoms of depression, as well as secondary symptoms such as appetite change, concentration problems and low self-esteem. However, it is important that future research replicates these effects in other samples and populations to improve generalizability.”
There are several possible reasons why muscle strength might help protect against depression. Lower muscle strength can lead to a loss of independence and greater difficulty completing daily tasks. Struggling with everyday activities is known to increase the likelihood of experiencing depressive symptoms.
Another possibility involves biology at the cellular level. When muscles contract during exercise, they release specific proteins into the body. Some scientists suspect these proteins might help protect the brain against depression, though more research is needed to confirm this.
The scientists noted a few potential misinterpretations and limitations. The people in the UK Biobank tend to be healthier and more educated than the average population, which might skew the results. The study also only included individuals of white European ancestry.
The scientists also used hand grip strength as a substitute for total body muscle strength. This is a common scientific practice, but there is an ongoing debate about how accurately hand strength reflects overall muscle power.
“We remain very interested in pursuing this line of research,” the researchers told PsyPost. “Our next steps will include examining both environmental and genetic factors related to depression and anxiety, as well as how the interplay between these factors can influence mental health.
“One important way in which our study moves the field forward is by examining individual depressive symptoms (in addition to depression as a single disorder). This approach may help researchers better understand the different pathways that contribute to depression and inform more targeted prevention strategies.”
The study, “Cardiorespiratory fitness, grip strength and depression symptoms: A Mendelian Randomization study,” was authored by John Vincent, Snehal M. Pinto Pereira, Jane Maddock, Dylan M. Williams, Mark Hamer, Jonathan P. Roiser, and Amy E. Taylor.
